In general, an electric motor includes a rotor, the moving component, and a stator, the stationary component. In one type of electric motor, commonly called an outer-rotor type motor, the rotor surrounds the stator and includes magnets. The stator includes windings carrying electrical current that interacts with the magnetic field of the rotor to generate forces that rotate the rotor about the stator. The outer-rotor type motor is suitable for use in electric fans, blowers, pumps, etc., in which the outer-rotor type motor rotates blades or other fluid-moving components about an axis to produce current or flow within a fluid (e.g., air or liquid). The outer-rotor type motor is also suitable for use in appliances, such as horizontal axis washing machines in which the rotor is used to directly drive the drum of the washing machine. In another type of electric motor, commonly called an inner-rotor type motor, the stator surrounds the rotor. The inner rotor rotates relative to the stator, using the same principles as the outer-rotor type motor. The inner-rotor type motor may also be used in electric fans, blowers, pumps, etc., or other applications.
Typically, the rotor of the motor must be balanced during manufacture and/or assembly to ensure that there is minimum interference (e.g., rubbing) between the rotor and stator, which can lead to vibrations, reduce efficiency due to frictional loses, or cause premature wear of other components (e.g., tub bearings in a washing machine). In one example, clay-like balancing putty may be used to balance the rotor. The balancing putty must adhere to the rotor (e.g., within a pre-formed cavity in the rotor) and remain adhered to the rotor. However, the balancing putty has a tendency to detach from the motor during balancing, or shortly thereafter, if the putty has not yet cured.